Hi Mr Skydive...... I am just being the devils advocate here and in no way trying to disrespect you at all.
A fully loaded Twin Otter will weigh close to what a back hoe weighs... The backhoe tires are ALOT wider, so they introduce less pounds per square inch of damage then the skinny tires the otter has on it. The otter travels faster across the ground in most of its operating range so rutting is not that apparent. The backhoe will work in a given spot and 'wallow' around and the damage is obvious. I can see from the pic you posted that the otter is sitting pretty on a piece of ground and that you guys already have fresh grass growth.. That is a good thing and a bad thing. Good meaning the grass is promoting growth of both above ground grass blade production and below ground root structure. When the runway is still wet, well ,,,,,,lets call it moist, it is still prone to rutting.
Even if it is slight and hidden, below the new grass growth the ruts are still there. When the runway dries out and the grass grows high the ruts made early on are now hidden... In a 'perfect storm' ie, the plane lands perfectly in the hidden ruts later is the summer when those ruts have hardened the potential of a plane getting squirlley is a possibility. I might be beating a almost dead horse here but I would hate to see you have a mess on your hands. I assume you will be rolling the runway to remove any imperfections ? This is just food for thought and worth exactly what you paid for it,, thats 0.00000